Microbial growth occurs in many systems in which aqueous media such as water, aqueous solutions and aqueous dispersions are employed.
For example, significant biofouling can occur in many areas of photoprocessing systems and, in particular, where low flow rate washes and water recycling is used. The problem may be overcome by adding biocides to the wash water tanks when bacterial biofilm formation becomes evident visually. However at this point the biocides may not work and even at quite high concentrations are not particularly effective because the bacteria have attached to surfaces to form colonies which have built up in layers. Hence, any biocide in solution can only reach the outer biofilm layer and not the inner layers of the biofilm which are protected. Furthermore, widespread use of such biocides is not desirable because they are relatively expensive and toxic chemicals which require specialised disposal to protect the environment.
Potentiating agents are known to improve the performance of hydrophilic biocides in solution. They include compounds or a combination of compounds that can enhance synergistically the effect of a biocide without necessarily having an antimicrobial effect of their own.
For example, U.S. Pat. No. 5,322,834 describes synergistic biocidal compositions of certain water soluble isothiazolin-3-ones with one or more potentiating agents.
In contrast to the use of biocides in solution, EP-A-0 733 304 describes a biocidal material comprising a biocide immobilised on a support characterised in that the biocide has a log P value of at least 1.5, the support has a hydrophobic surface and the biocide is immobilised on the hydrophobic surface by hydrophobic exclusion. The support may take the form of polymer beads which may be held in a container having an inlet and an outlet so that the aqueous medium to be treated can be contacted with the beads by passing it through the container. An advantage of the material is that the hydrophobic biocide remains attached to the support during use i.e. there is no free biocide in solution. The material may be used to inhibit microbial growth in the wash water or other solutions used in a photoprocessor.
The immobilised hydrophobic biocides are believed to reach their site of action in a different way to the hydrophilic biocides. It is clear that hydrophobic biocides must operate by a different mechanism to hydrophilic biocides because of their different characters. The use of potentiating agents in combination with hydrophobic biocides is unknown and there is no reason to suppose that potentiating agents for the known water soluble biocides would be effective in combination with the immobilised biocides.